Abstract

Purpose : To compare, in a cross-sectional prospective study, the resilience to increased intraocular straylight (IOS) of four energy modulation stimuli designed to probe changes in spatial summation in glaucoma.
Methods : Threshold (ΔE) was measured at 18 visual field locations in one eye of three young, healthy, psychophysically-experienced observers with normal media [age: 25, 31, 33 years], using four different energy modulation stimuli, each under four different levels of IOS. Stimuli were: A - fixed contrast (ΔI: 0.5, starting within Ricco’s area), varying in area; C1 - fixed area (0.02 deg2, within Ricco’s area), varying in contrast; AC - varying in both area and contrast simultaneously (starting within Ricco’s area); C2 - fixed area (0.15 deg2), equivalent to Goldmann III, varying in contrast. Step sizes (energy; luminance x area x duration) were equivalent for each stimulus. IOS was measured with an Oculus C-Quant (Oculus, Wetzlar, Germany) for each participant with each of three filters of increasing white opacity (filters 1, 3, and 5, LEE filters, Andover, UK), and with no filter (baseline), in a randomised order. Stimulus type and filters were randomised between all threshold tests. Mean visual field threshold was calculated for each participant and between participants, and plotted as a function of IOS.
Results : Mean IOS at baseline was 1.2 log(s). Filter 5 (greatest opacity) gave a mean IOS of 2.0 log(s). Simulated ages, calculated from normative IOS values (van den Berg et al, Am J Ophthalmol, 2007;144(3):358-63), are given in Fig.1. An increase in mean ΔE with increasing IOS was found for all stimuli, but was greatest for C1 and C2 stimuli, particularly with low/moderate levels of IOS (Fig.1). Mean ΔE for A and AC stimuli, were significantly lower than those for C1 and C2 stimuli with filters 1 and 3 (all p<0.05). The smallest increase in ΔE, and greatest resilience to moderate increases in IOS was found for stimuli in which area was modulated (A and AC). The overall effect persisted in individual participants’ data.
Conclusions : Area-modulated perimetric stimuli showed greater resilience to increased IOS, compared to conventional perimetric stimuli of fixed area, modulating in contrast, at least over the normal range of IOS expected across the typical human lifespan.